Electron discharge devices and cathodes therefor



Jan. 27, 1959 J. M. osEPcHUK 2,871,394

ELECTRON DISCHARGE DEVICES AND CATHODES THEREFOR supPLv 439 FILAMENT 2 Sheets-Sheel 2 Jan. 27, 1959 J. M. OSEPCHUK ELECTRDN DISCHARGE DEVICES AND CATHDDEJS THEREFOR Filed Nov. 28, 1955 ELEC'ERGN DHSCHARGE DEVICES AND CATHQDES THEREFR .lohn M. Gsepehnh, Peabody, Mass., assigner to Raytheon Manufacturing Company, Waltham, Mass., a corporation of Delaware Application November 2S, 1955, Serial No. 549,326

13 Claims. (Cl. S15-3.5)

This invention relates to electron discharge devices, and more particularly to high frequency amplifying or oscillation-generating devices or" the magnetron type and their cathodes.

ln this type of tube, a beam of electrons is emitted by a cathode toward an anode structure maintained at a potential positive with respect to the cathode and formed with a plurality of resonant cavities so that it forms a periodic frequency responsive energy translatio-n strueture for transmitted signal. The anode may be in the form of a helix in what are known as traveling wave tubes, or it may be formed with a series of vanes to form a series of cavities. An electrode, called a sole, is mounted parallel to the anode and is usually'rnaintained at the cathode potential. When such a tube is operated as an amplifier, there is a collector electrode at the end of the anode maintained at a potential positive with respect to the cathode. A magnetic iield is arranged transverse to the electron stream. ln the oscillator version, radio frequency energy is generated in the anode structure at a frequency determined in part by the potential between the cathode and the anode. lt is desirable in this type of tube that the electron beam be a thin ribbon. Such a beam might be obtained from a very thin filamentary cathode, but such a catho-de is mechanically ditiicult to construct, mount, and protect from breakage and burn-out.

Bf the present invention, a cavity is formed either in the second electrode, or sole, or associated with it, with its axis transverse to that of the sole and with a narrow slit connecting its interior to the interaction space. The walls of this cavity are coated with electron-emissive niaterial. A heater is mounted at the center and either maintained at a potential that is positive with respect to the sole and the cathode coating, or insulatedly mounte on an electrode that is maintained at such a potential.. The resulting electrons form a space charge that tends to penetrate into the slot in the presence of a potential on the main anode or transmission line, positive with respect to the sole and a transverse magnetic eld. A portion of this charge, dependent upon the applied potential and magnetic held and the width of the slot will be pulled through the slot and moved down the transi mission line to the collector in a thin, highly concentrated beam. As the thickness of this beam is determined largerly by the width of the slot, and this width can be relatively easily controlled by well-known machining techniques, it is easier to obtain the dense beam of electrons tot a tube of this type with this type of cathode structure.

Other and further advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawings wherein:

Fig. l is a transverse cross section of a jiirst embodiment ot this invention wherein the anode structure is arranged in a straight line;

Fig. 2 is a section along the line 2 2 of Fig. l;

Fig. 3 is a detail of the cathode of Figs. 1 and 2;

'ice

Fig. 4 is a section taken along the line 4-4 of Fig. 3;

Fig. 5 is a plan view of the section shown in Fig. 3;

Fig. 6 is a modification of the cathode shown in Figs. 4 and l5; and

Fig. 7 is a modification of the cathode and related structures shown in Figs. 1 and 2.

In Fig. l, the reference numeral 10 designates a linear traveling wave amplifier of the magnetron type comprising an upper plate 11, a lower plate 12, side plates 13 and'end plates 14, all of conducting material, such as copper, to form a conductive evacuated envelope. Extended downward from the plate 11 is a plurality of anode members 15, which are shown here, for example, as substantially rectangular planar members. Other Wellknown configurations may be used. In these, anode members 15 are rigidly attached at their upper ends to the top plate 11 and are alternately connected at points on their edges adjacent their lower ends by conductive straps 16, according to well-known practices in magnetron tubes. The planar members 15 are positioned substantially'perpendicular to the support member 11 and to the conductive straps 16.

Positioned inside the envelope 1d, adjacent and parallel to the lower edges of anode members 15, is a metallic plate or sole 17. Sole 17 is supported by means of insulated support 18 and insulated connector 20. Connector Ztl provides electrical connection of sole 17 to the negative terminal of. a source 21 of anode supply but prevents electrical Contact of the sole 17 with the envelope itl.

A collector electrode 22 is positioned at the right hand endrof the sole 17 and the vanes 15 by an insulated support 23 and is connected to the positive terminal of the anode supply 21.

Coaxial probe 24 connects the line to an impedancematched termination 25 through a connector 26. The outer conductor 24a of this line connects to the end vane 15, and the inner conductor 24h connects to the next to last vane 15. A second coaxial probe 27 connects the line to an output load 2S through a connector Eil.

A cylindrical cavity 31 is formed transversely in the sole 17 and connected to the surface of the sole that is nearest the vanes 15 by means of a transverse slot 32. The wall of the cavity is coated with a layer 33 of electron-emissive material. A rod 34 is mounted along the axis of the cavity 31 on two discs 35 of insulating material.-V This rod Mis connected to a source of positive potential over a conductor 36, as shown in Fig. 2. A filament 37 with an insulating coating 3S is wound about the'rod 34` and connected to a source 3S of iilament supply overconductors 40.

A transverse magnetic iield is applied by means of pole pieces'41, as v,seen in Fig. 2, to the full extent of the.

interaction space.

The rod 34 operates as an auxiliary anode. When electrons areemitted by the coating 33 heated by the lilament 37 .in the transverse magnetic field caused by the pole pieces 41, and with a less than cut-ott potential dir" ference between the anode 34 and cathode 33, they are caused` to yfollow a curved path from the cathode and back to the cathode, as indicated by the line 42 in Fig. 3, as in a magnetron with such fields. These electrons form a space charge, as indicated by the dotted area 43 of Fig. 3. Some of these electrons will have a component of radial velocity that will drive them into the slit 32, where they come under the inliuence of the potential difference between the-anode vanes 15 and the sole 17 and the transverse magnetic lield caused by the pole pieces aetnanet collector 2.2 along a path indicated by the doted line 45 in Fig. l.

As shown in Fig. 6, the lament 37 may form the anode of the auxiliary magnetron formedin, the cavity by omitting the rod 34 of Figs. 3, 4, and 5 and conne.cting one of the conductors v4@ from .the iilamenltl37; .to Aa source i7 of positive potential. The operationmwill be the same with this construction. Other.. methods of .heat-J ing the cathode than that shown may, beusedm The cathode of this invention may be formed as a holy.. low cylinder 48, as shown in Fig, 7', WithUa-coating of electron-emissive material and a slitS, as before, to form an auxiliary magnetron again with less than cutfy oi anode potential. Sti with the auxiliary magnetron positioned with the auxiliary anode Si, and the slit 50 aligned 4with the space between the anode varies 15and Ythesole v17 along the axis of the tube iii will follow a cycloida l path, whicl 1 is undesirable as it prevents the formation ofthe desired thin stream of electrons. To prevent this, an electrode 52 is formed with an aperture 53 aligned withv theslit t) and maintained at a positivepotential with respect to the cylinder i3 by means of a source'SfiY of potential. Configurations other than the'rod 51 yand cylinder 4S could be used for the auxiliary magnetron.

In Fig. l, the tube is shown with a sole 17 and anodey i5 arranged in straight lines. lt is apparent that the tube could be arranged about a circle, as shown in Figs. 3 and 4 of the United States Patent No. 2,673,306 to W. C. Brown. i While an amplifier has been shown in Figs. l and 2, this type of cathode construction could be used in forward or backward wave oscillators as well.

This invention is not limited to thev particular details of constructiom materials and ,processes described, as` many equivalents will suggest themselves to those skilled in the art.

rihe electrons emitted from the slit l,

It is accordingly -idesired that the appended claims be given a broad interpretation commensurate with beam-forming means comprising a cylindrical electronemissive cathode electrically-connected to said principal electrode and disposed about a conductor maintained at a potential positive with respect to that ofthe cathode, the axis of said cathode being arranged parallel to the magnetic i'leld and an auxiliary electrodeVmaintained at a potential positive with respect to rsaid cathode to form an electrical eld at right angles to said ymagnetic eld.

2. A traveling wave tube omprising'a periodic frequency-responsive energytranslation structure for trans mitted signals, a principal electrode spaced from and substantially coextensive with said translation structure and adapted to be maintained at a potential negative with respect thereto to form anelectrical eld, means to apply a magnetic iield at right angles to said electrical eld, l

beam-forming means comprising a cylindrical electronemissive cathode formed with aslit, said cathode being electrically connected to said principal electrode and disposed about a conductor adapted yto be maintained at a potential positive with respectto that of the cathode` and with its axis arranged parllel to the magnetic. field, f, an auxiliary electrode maintained. at a potential posi-- tive with respect to said cathodeto forman electricalY eld at right angles to said magnetic field and an acceyl...y

erating electrode formed with an opening and positioned;`

quency-responsive energy translation structure for trans- -mitted signals, a principal electrode spaced from and form an electrical fleldat right angles to said magnetic iield.

4. A traveling wave tube comprising a periodic trequency-responsive energy translation structure for trans mitted signals, a principal electrodek spaced from and substantially coextensive with said translation structure and adapted to be maintained at a potential negative with respect. thereto to` form an electrical field, means to apply a magnetic field at right anglesto said electrical field,v beamrforming means comprising; an electron-.emissiwe cathode formed as a transverse cylindrical opening in said principal electrode connected to the surface of said electrode adjacent said translation structure by means of a slit, heating means for said cavity, and an electronemissive coating on the walls of said cavity.

5. A traveling wave tube comprising a periodic frequency-responsive energy translation structure for transmitted signals, a principal electrode spaced from and substantially coextensive with said`translation structure and adapted to .be maintained at a potential negative with respect thereto to form an electricalileld, means to apply a magnetic iield at right angles to said electrical eld, beam-forming means comprising an electron-emissi-ve cathode formed as a transverse opening in said principal electrode, a rod'insulatedly'mounted on said principal electrode coaxially within said cathode and maintained at a potential. positive with respect to said cathode, and

heating means lfor said cathode maintained ata potential positive with respect to saidcathode.

6. A traveling wave tube comprising a periodic frequency-responsive energy translation structure for transmitted signals, a principal electrode spaced from and substantially coextensive with said translation structure and adapted to be maintained at a potential negative with respect thereto to form an electrical field, means to apply a magnetic field at right angles to said electrical iield, beam-forming means comprising an electron-emissivel cathode formed as a transverse opening in said principal electrode connected to the surface of said electrode adjacent said translation structure and a heating elementA quency-responsive energy translation structure for transmitted signals, a principal electrode spaced'fro'm andV substantially coextensive with said translation structure and adapted to be maintained at a potential negative with respect thereto to form an electrical eld,.means to apply a magnetic iield at right angles to said electrical field, beam-forming means comprising an electron-emissive cathode formed as a transverse cylindrical opening in said principal electrode, a rod insulatedly mounted on said principal electrode coaxially within said opening,

and a heating element axially insulatedly .mounted in said opening about said rod.

8. A traveling wave tube comprising a periodic frequency-responsive energy translation structure for transmitted signals, a principal electrode spaced from and substantially coextensive with said translation structure and adapted to be maintained at a potential negative with re.` spect thereto to form an electrical field, means to apply a magnetic field at right 'angles to said electrical field, beam-forming. means comprising an electron-emissive cathode formed as a transverse opening in said principal.

electrode connected to the surface of said electrode adjacent said translation structure and a heating element axially insulatedly mounted on said principal electrode in said opening adapted to be maintained at a positive potential less than the critical potential with respect to said cathode.

9. A traveling wave tube comprising a periodic frequency-responsive energy translation structure for transmitted signals, a principal electrode spaced from and substantially coextensive with said translation structure and adapted to be maintained at a potential negative with respect thereto to form an electrical eld, means to apply a magnetic field at right angles to said electrical field, beam-forming means comprising an electron-emissive cathode formed as a transverse opening in said principal electrode, a rod insulatedly mounted on said principal electrode coaxially within said opening, a heating element axially insulatedly mounted on said principal electrode in said opening about said rod, and means to maintain said rod at a positive potential less than the critical potential with respect to said cathode.

l0. An electron source for a traveling wave tube having a periodic, frequency-responsive anode, a principal electrode arranged parallel thereto to form an electrical field and means to apply a magnetic field at right angles to said electrical field, comprising a cathode formed asy an electron-emissive coating on a cylindrical surface with its axis parallel to the magnetic field enclosing a -coaxially mounted conductor adapted to be maintained at a positive potential with respect to said cathode and heating means.

l1. An electron source for a traveling wave tube having a periodic, frequency-responsive anode, a principal electrode arranged parallel thereto to form an electrical field and means to apply a magnetic field at right angles to said electrical field, comprising a cathode formed as an electron-emissive coating on a cylindrical surface with its axis parallel to the magnetic field enclosing a coaxially mounted conductor adapted to be maintained at a positive potential with respect to said cathode, an accelerating electrode formed With an opening and positioned beyond said electron source and adapted to be maintained at a positive potential with respect to said electron source, and heating means for said cavity.

l2. An electron source for a traveling Wave tube having a periodic frequency-responsive anode, a principal electrode arranged parallel thereto to form an electrical iield and means to apply a magnetic field at right angles to said electrical field, comprising a cathode formed as an electron-emissive coating on the walls of a transverse opening formed in said principal electrode connected to the surface of said electrode adjacent said anode, and heating means for said cathode.

13. An electron source for a traveling wave tube having a periodic, frequency-responsive anode, a principal electrode arranged parallel thereto to form an electrical field and means to apply a magnetic eld at right angles to said electrical field, comprising a cathode formed as an electron-emissive coating on the Walls of a transverse cylindrical opening formed in said principal electrode an electron-emissive coating on the walls of a transverse opening formed in said principal electrode connected to the surface of said electrode adjacent said anode, a rod insulatedly mounted on said principal electrode coaxially within said cavity, and heating means for said cathode.

l5 Anelectron source for a traveling Wave tube having a periodic, frequency-responsive anode, a principal electrode arranged parallel thereto to form an electrical eld and means to apply a magnetic ield at right angles to said electrical field, comprising a cathode formed as an electron-emissive coating on the walls of a transverse opening formed in said principal electrode connected to the surface of said electrode adjacent said anode, and a heating element axially insulatedly mounted on said principal electrode in said cathode adapted to be maintained at a positive potential with respect to said cathode.

16. An electron source for a traveling wave tube having a periodic, frequency-responsive anode, a principal electrode arranged parallel thereto to form an electrical field and means to apply a magnetic eld at right angles to said electrical field, comprising a cathode formed as an electron-emissive coating on the walls of a transverse cylindrical opening formed in said principal electrode connected to the surface of said electrode adjacent said anode, a rod insulatedly mounted on said principal electrode coaxially Within said cathode and adapted to be maintained at a positive potential with respect to the cathode, and a heating element axially insulatedly mounted in said cathode.

17. An electron source for a traveling wave tube having a periodic, frequency-responsive anode, a principal electrode arranged parallel thereto to form an electrical ield and means to apply a magnetic field at right angles to said electrical field, comprising a cathode formed as an electron-emissive coating on the walls of a transverse cylindrical opening formed in said principal electrode connected to the surface of said electrode adjacent said anode, and a heating element axially mounted on said principal electrode in said cathode adapted to be maintained at a positive potential less than the critical potential with respect to said cathode.

18. An electron source for a traveling wave tube having a periodic, frequency-responsive anode, a principal electrode arranged parallel thereto to form an electrical References Cited in the ile of this patent UNITED STATES PATENTS 1,790,153 Hull Ian. 27, 1931 2,009,839 Found July 30, 1935 2,622,158 Ludi Dec. 16, 1952 2,694,783 Charles Nov. 16, 1954 2,761,088 Warnecke et al. Aug. 28, 1956 2,807,739 Berterottiere et al Sept. 24, 1957 2,809,328 Dench Oct. 8, 1957 2,813,990

Robertson Nov. 19, 1957 

